Patellofemoral pain: Comparable effectiveness of exercises, effect modifiers, and agreement of visual assessments

Introduction: International consensus based on current evidence advocate the use of resistance training for the lower extremities for the treatment of patients with patellofemoral pain (PFP). But direct comparisons of exercise modalities are few, sample sizes are small, and intervention- and follow-up periods have been short. Collectively, this challenges the choice of the most effective treatment for the patient group. Moreover, the PFP population is very heterogenous and a ‘one-size-fits-all’ approach presumably is not optimal. We need to identify patient characteristics that can predict a superior outcome from one specific treatment over the other. One of these potential characteristics is functional alignment of the knee. However, the reproducibility of assessing functional knee alignment in patients with PFP in the clinic has not been established.
Purpose: The primary purpose of this PhD project was to investigate the comparable effectiveness of two commonly prescribed exercise protocols on symptoms and physical function for patients with PFP. Further, we aimed to assess which patient characteristics that predict a better outcome of one of the exercise protocols over the other. As a final purpose, we wanted to investigate the intra- and interrater agreement for visual assessments of knee alignment during a single-leg squat (SLS) and a forward lunge (FL).

Methods: To address the purposes set above, three studies were completed. First, a randomized clinical equivalence trial exploring the comparable effectiveness of a hip focused vs a quadriceps focused exercise program was conducted (Study 1). Secondly, a post-hoc analysis exploring the interaction between certain pre-specified patient characteristics and group allocation was performed (Study 2). Finally, we conducted a cross-sectional agreement study to establish the reproducibility of visual assessments of knee alignment (Study 3).

In Study 1, we included 200 participants diagnosed with PFP. They were randomly allocated to either quadriceps focused exercises (QE), including squat, lunge, and knee extension or hip muscle focused exercises (HE), including hip abductions, clam-shell, and hip extensions. Upon an instructional consultation, participants did their exercises three times per week at home with monthly clinical visits at the clinic. The primary outcome was change from baseline in the Anterior Knee Pain Scale (AKPS) at week 12. Secondary outcomes included change in the Knee injury and Osteoarthritis Outcome Score (KOOS), isometric muscle strength, Dynamic Assessment of Pain (DAP), Pain Self-Efficacy Questionnaire, the 3-level version of EuroQoL 5 dimensions (EQ-5D-3L) Questionnaire, and The Transition Questionnaire of global perceived effect on overall health, pain, and function at week 12. Change from baseline in questionnaire data was re-assessed at week 26.

In Study 2, we performed a post-hoc analysis on the population from the main trial. Primary outcome was the AKPS at week 12, and the candidate baseline characteristics encompassed a range of self-reported information as well as clinical observations. The analyses focused on the interaction between presence/absence of the patient characteristics and group allocation (QE vs. HE) at each time point (week 12 and 26).

In Study 3, we included the first 60 participants from the main study. A video was recorded using a tablet from an anterior view of participants performing the SLS and FL. The investigator scored the movement as observed clinically according to preset criteria (valgus, varus, or no malalignment). At least one week later, the investigator did another scoring based on the recorded video and another investigator repeated the scoring independently. Cohen’s weighted kappa statistics was used to assess the intra- and interrater agreement.

Findings: We included 200 participants for Study 1 and 2 (mean age 27.2 years, SD 6.4); 60 of these were included for Study 3. Mean changes in AKPS questionnaire score from baseline to week 12 were 7.5 (SE ±0.8) for QE and 7.2 (SE ±0.8) for HE. The 95% CI of the group difference in change in AKPS questionnaire from baseline to week 12 was within the predefined equivalence margin of±8 points; p
Conclusion: We found that an exercise program that focused on either quadriceps or hip muscles provided equivalent improvements in symptoms and function in the short (12 weeks) and medium term (26 weeks). Further, we found that participants with pain catastrophizing or a high BMI benefitted more from quadriceps exercises than from hip exercises, whereas hip exercises were better for patients with more severe knee pain at baseline. Lastly, we found moderate to good intrarater agreement visually assessing dynamic knee alignment during SLS and FL, whereas the interrater agreement ranged from fair to moderate.